The electroless plating has been known as the method for giving electric conductivity and metallic luster to a resin material. This electroless plating is the method of chemically reducing metal ions in a solution, and depositing a metal coating on a surface of a material, and with this method, a metal coating can be formed on an insulator such as resins, too, as is different from electroplating of depositing a metal coating by electrolysis with electric power. In addition, electroplating can be carried out on the resin material on which a metal coating has been formed with electroless plating, thereby enlarging the use of the resin material. For these reasons, the electroless plating has been widely used as the method for giving metallic luster and/or electric conductivity to the resin material for use in various fields such as parts of motor vehicles, household electric appliances, etc.
The plated coating formed with electroless plating, however, has the problems that it takes a considerable time to form the coating, and the adhesion of the coating against the resin material are not sufficient. In order to solve these problems, there have been generally carried out the processes of first chemically etching the resin material to roughen the surface thereof, and then electroless plating the chemically etched resin material.
Furthermore, Japanese unexamined patent publication No. Hei 1-092377 discloses the method of previously treating a resin material with an ozone gas, and then electroless plating the treated resin material. In accordance with this publication, unsaturated bonds in the resin material are unbound to be changed to low molecules, and consequently, molecules having different chemical compositions coexist on a surface of the resin material, whereby the smoothness thereof is lost, and the surface is roughened. Accordingly, the coating formed with electroless plating tightly enter the roughened surface to prevent the coating to readily peel off therefrom.
In the above-described conventional methods, the adhesion of the plated coatings is enhanced with a so-called anchor effect by roughening surfaces of the resin materials. With these methods, however, the surface smoothness of the resin materials decreases. Accordingly, in order to obtain a metallic luster which gives good appearance to the resin materials, the plated coatings must be thick to cause the disadvantage of an increment of manufacturing time.
In addition, in the method of roughening the surface of the resin material by etching, hazardous substances such as chromic acid, sulfuric acid, etc. must be used, and accordingly, there arises problems in the treatment of resultant liquid waste, etc.
The present invention has been made considering these problems of the conventional methods, and has an object of obtaining the method capable of forming a plated coating exhibiting excellent adhesion without roughening a surface of a resin material by etching or ozone gas treatment.
The pretreatment method for an electroless plating material in accordance with the present invention, which is capable of solving the above problems, is characterized by a first treating process of bringing a plating material composed of a resin having unsaturated bonds into contact with a first solution which contains ozone, and a second treating process of bringing a second solution which contains at least one of an anionic surface active agent and a nonionic surface active agent, and an alkaline component into contact with the plating material being carried out.
It is desirable that the first solution contains 50 PPM or more of ozone, and it is desirable that the first solution contains a polar solvent. In addition, it is preferable that the treating temperature in the first treating process is approximately room temperature, and in this case, it is preferable that the treating temperature in the second treating process is higher than that in the first treating process. Furthermore, it is preferable that the concentration of the surface active agent in the second solution ranges from 0.01 to 10 g/L.